1. Field of the Invention
The present invention relates to a so-called optical element capable of controlling its light scattering amount, reflection amount, absorption amount or transmittance amount in response to electric signals. The optical element of the present invention is useful when adapted to color display devices for displaying images or characters, variable color filters, light modulation elements, light modulation glasses, interior materials or building materials.
2. Description of the Related Art
The technique employed for a light modulation element or display device capable of controlling a light scattering amount, reflection amount, absorption amount or transmittance amount by making use of a polymer gel which reversibly expands or contracts under external stimuli has so far been reported in the below-described patent gazettes.
For example, in Japanese Published Unexamined Patent Application No. Hei 4-134325, proposed is an element which controls a light scattering condition by a density change of a polymer gel expanded or contracted by energization, thereby conducting light modulation or display, depending on opaqueness or transparency. In Japanese Published Unexamined Patent Application No. Hei 5-188354, proposed is an element which makes the particle size of polymer gel particles larger or smaller than the wavelength of light by swelling or contracting the polymer gel particles by energization, thereby conducting light modulation depending on opaqueness or transparency.
In Japanese Published Unexamined Patent Application No. Hei 4-274480, proposed is an optical element which utilizes energization-induced expansion or contraction of a colored polymer gel covalently bonded with a dye. In this application, disclosed is an optical element technique which causes an increase or decrease of an optical absorption cross-sectional area depending on expansion or contraction of the polymer gel due to energization, thereby changing an optical density in Japanese Published Unexamined Patent Application No. Hei 9-160081, proposed is an optical element using a colored substrate and a colored polymer gel in combination. In this application, disclosed is an optical element technique which increases or decreases its optical density by changing a covering ratio of the colored substrate with the colored polymer gel by bending or stretching, or by expanding or contracting the colored polymer gel under electric stimuli.
In Japanese Published Unexamined Patent Application No. Sho 61-149926 and Japanese Published Examined Patent Application No. Hei 795172, proposed is an optical element made up of a composition using in combination a polymer gel which expands or contracts by energization and a colored liquid having a pigment dispersed therein. In Japanese Published Unexamined Patent Application No. Sho 61-149926, disclosed is a technique for utilizing a change in an optical absorption amount of a colored liquid which change occurs at the time when transfer of the colored liquid is caused by a change in the form of the polymer gel by energization. In Japanese Published Examined Patent Application No. Hei 7-95172, disclosed is a technique for preventing electrolysis of a colored liquid, which will otherwise occur by energization, by employing a conductive polymer as an electrode, thereby becoming free from generation of air bubbles due to electrolysis.
In Japanese Published Unexamined Patent Application No. Hei 11-236559, the present inventors proposed an optical element and display device each making use of expanding or contracting properties, under external stimuli, of a polymer gel which contains a pigment at a concentration not less than a saturated absorption concentration. In Japanese Published Unexamined Patent Application No. Hei 11-236559, disclosed is a technique of causing agglomeration or diffusion dispersion of the pigment by expansion or contraction of the polymer gel by energization, thereby causing a change in optical density. In Japanese Published Unexamined Patent Application No. Hei 11-236559, similar to Japanese Published Examined Patent Application No. Hei 7-95172, a technique of employing a conductive polymer as an electrode is disclosed.
The light modulation or display device as disclosed in the above-exemplified official gazettes however has various problems to be overcome.
For example, the elements as disclosed in Japanese Published Unexamined Patent Applications Nos. Hei 4-134325, Hei 5-188354, Hei 4274480, Hei 9-160081 and Sho 61-149926 are accompanied with the problem that whenever a current is supplied, the display quality or light modulation properties are impaired by air bubbles generated upon electrolysis of a liquid emitted from or absorbed in the polymer gel.
Elements, as disclosed in Japanese Published Examined Patent Application No. Hei 7-95172 and Japanese Published Unexamined Patent Application No. Hei 11-236559, which adopt a conductive polymer as an electrode in order to prevent generation of air bubbles due to electrolysis of a liquid are also accompanied with the problem that a sufficient display contrast or a sufficient change in reflectance or light absorption amount cannot be attained owing to a color intrinsic to the conductive polymer adopted as the electrode. In addition, the conductive polymer tends to be deteriorated whenever a current is supplied so that poor durability of the element upon energization still remains as a problem.
In view of the problems of the related art noted above, the present invention has been made to provide a novel optical element which undergoes a sufficiently large change in a light scattering ratio, reflectance or light absorption amount and in addition, exhibits stability upon repeated use; and also to provide an optical element which has a constitution permitting easy fabrication.
The present invention can be attained by the below-described optical elements, optical element composition and method of controlling a stimuli-responsive polymer gel.
In one aspect of the present invention, there is thus provided an optical element including plural electrodes and disposed therebetween, a stimuli-responsive polymer gel which expands or contracts under external stimuli, a liquid which can be absorbed therein and an ion supplying material having a property of delivering or receiving ions in response to at least an electric field.
An optical element having, as the ion supplying material, a material undergoing, in the form of the optical element, a volumetric change of 0 to 100% in response to external stimuli is preferred. An optical element having an ion conductive material as the ion supplying material is more preferred. As the ion conductive material, that undergoing a change in its internal pH according to the concentration of ions contained therein is preferred, with an ion exchange resin being more preferred.
An optical element having the ion supplying material disposed in the vicinity of at least one of the plural electrodes is preferred, with that having the ion supplying material in the film form being more preferred. An optical element having the ion supplying material of 10 mm to 0.01 xcexcm in film thickness, particularly, the ion supplying material having a smooth surface is preferred. Moreover, an optical element having at least one of the plural electrodes onto which electric insulation treatment has been applied is preferred.
An optical element having the stimuli-responsive polymer gel disposed in the vicinity of the ion supplying material is preferred, with that having the stimuli-responsive polymer gel contained in the ion supplying material being more preferred.
An optical element having a polyelectrolyte gel as the stimuli-responsive polymer get is preferred, of which the stimuli-responsive polymer gel containing a light modulation material is more preferred. Also provided is an optical element wherein the concentration of the light modulation material contained in the stimuli-responsive polymer gel is not less than a saturated absorption concentration or not loss than a saturated scattering concentration upon contraction of the stimuli-responsive polymer gel. Preferred is an optical element having the stimuli-responsive polymer gel which increases its volume upon expansion by at least 5 times compared with that upon contraction.
In another aspect of the present invention, there is also provided an optical element composition, which includes an ion supplying material having a property of delivering or receiving ions in response to at least an electric field, a stimuli-responsive polymer gel and a liquid which can be absorbed therein. An optical element composition having the stimuli-responsive polymer gel incorporated in the ion supplying material is also provided.
In a further aspect of the present invention, there is also provided a method for controlling a stimuli-responsive polymer gel, which includes controlling expansion or contraction of the stimuli-responsive polymer gel based on the delivery or receipt of ions from an ion supply material source having a property of delivering or receiving ions in response to at least an electric field.
In the optical element of the present invention, ions are emitted from or adsorbed to the ion supplying material disposed in the element by the application of an electric field between electrode substrates, leading to a change in the ion concentration of the electrolyte solution. When a material undergoing a change in its internal pH depending on the ion concentration is disposed as an ion supplying material, the pH of the electrolyte solution in the vicinity of the ion supplying material can be changed by increasing or decreasing the ion content in response to an electric field.
In the optical element according to the present invention, since the stimuli-responsive polymer gel filled between the substrates is responsive to this change in the ion concentration or in pH, it can be expanded or contracted in response to an electric field. The polymer gel undergoes a large change in the optical density depending on expansion and contraction so that the optical element of the present invention is capable of causing a large change in the optical density by a volumetric change of the polymer gel in response to an electric field.
Since the optical element of the present invention uses neither electrolysis of water which generates air bubbles and therefore causes a problem in the durability of the element nor a colored conductive polymer which is a cause for impairing optical properties of the element, light modulation or display with a high contrast can be actualized easily.
As described above, the optical element according to the present invention undergoes a large change in an optical scattering ratio, reflectance and absorption amount and has stability upon repeated use. Thus, it is excellent as an optical element.